This is a multicenter, randomized, double-blind, placebo-controlled, parallel-group, Phase 2 exploratory study in adult subjects with childhood onset fluency disorder.

At the Baseline visit, eligible subjects will be randomized 1:1 to receive either a target steady-state dose of ecopipam HCl ~2 mg/kg/day or matching placebo for a 12-week Treatment Period consisting of a 4-week Titration Phase followed by an 8-week Maintenance Phase.

Subjects will return to the clinic at 4, 8, and 12 weeks after Randomization and Follow-up visits 7 and 14 days after completing the Treatment Period or Early Discontinuation. Efficacy assessments will be conducted at Weeks 4, 8, and 12 and safety assessments will be conducted at all visits. Subjects will have adverse events and other safety parameters assessed by phone or video conference at Weeks 2, 6 and 10 and 30 days after the last study drug administration. Signs or symptoms of withdrawal, abuse, and dependence will be monitored throughout the study.

At the end of the Treatment Period or Early Discontinuation, subjects will taper study drug by 25 mg/day until off study drug, for up to 1 week.

Inclusion Criteria:

• Able to read and write in English and provide informed consent
• 18 years or older of age at screening
• Weighs >= 45 kg (~99 lbs)
• Satisfies DSM-5 criteria for childhood onset fluency disorder
• History of stuttering for >=2 years with onset consistent to developmental in nature
• Must meet an allowed severity of stuttering at screening and baseline, scored by a central rater
• Completed an adequate course of speech therapy
• Has a qualifying IOS or Android smartphone
• Must discontinue all medications used to treat stuttering for at least 14 days prior to screening
• Sexually active females of child bearing potential must be using effective contraception during and 30 days after participation
• Sexually active males must use a double barrier method of contraception during and 30 days after participation

Exclusion Criteria:

• Stuttering is related to a known neurological cause
• Initiation of new behavioral therapies for stuttering within 10 weeks prior to baseline
• Unstable medical illness or clinically significant abnormalities on screening tests/exams
• At a significant risk of committing suicide
• Are pregnant or lactating
• Positive urine drug screen
• Lifetime history of major depressive episode
• History of seizures
• Have been previously treated with ecopipam
• Unstable use of medications prior to screening
• Use of prohibited medications or need for medications which would have unfavorable interactions with ecopipam
• Not suitable for study in the opinion of the Principle Investigator